1. Field of the Invention
This invention relates generally to electronic data processing, and pertains more particularly to a system for transmitting digital data over a longer distance than conventional data channels permit. In its most preferred form, this invention contemplates temporary storage of data and special logic to control or facilitate passage of the same to an external device.
2. Description of the Prior Art
Conventional wired data channels vary in length, the length usually being limited to a maximum of about 200 feet. Basically, the distance must be relatively short owing to two factors: (1) circuit limitations and (2) timing limitations.
(1) Circuit limitations occur from the attenuation of a signal as it progresses over a long wire, and also from skewing wherein several signals propagating in parallel may not reach their destination simultaneously.
(2) Timing limitations, on the other hand, result from the adoption of short propagation intervals. More specifically, where a set of signals must first propagate the entire length of a wire channel and a response signal propagate back over a second wire channel before further transmission can take place, the sum of these propagation times becomes greater than the interval at which the peripheral unit must be responded to, and a loss of data results.
Serialization of the data transmission has been a step in the proper direction as far as reducing the above-mentioned circuit limitations. Also, as far as parallel lines are concerned, channel extenders have been devised, these being long line drivers without utilizing serialization; but use of these results in a slowdown of data transfer which can trigger an error condition in a time sequence of demand receiver.